The present invention relates to a rubber composition for a tire enabling preparation of a tire in which grip performance and abrasion resistance are improved, and a tire using the same.
Recently, consciousness for safety has been enhanced in accordance with high power of automobile movement performance and development of express way. In particular, the grip performance represented by acceleration performance and brake performance is an important requisite property.
The compatibility of high grip performance and abrasion resistance is generally required for a tread rubber of a high performance tire. In order to obtain a rubber composition exhibiting high grip performance, it has been conventionally carried out that, for example, a styrene-butadiene rubber (SBR) having a high glass transition temperature (Tg) is used, equal amounts of a process oil and a resin with a high softening point are substituted and compounded, a softening agent and carbon black are highly filled, a softening agent and carbon black are used in combination, and silica is compounded.
However, a rubber composition using SBR having a high Tg has large temperature dependency, thus, change in performance for temperature change is enlarged, which causes a problem that a tire becomes fragile to be broken. Further, when equal amounts of a process oil and a resin with a high softening point is substituted, if the substitution amount is large, there is a problem that temperature dependency is large due to the influence of the resin with a high softening point. Further, when a large amount of a softening agent such as an oil is compounded, there is a problem that abrasion resistance is lowered. Further, when fine particle carbon black and a large amount of a softening agent are used, there is a problem that dispersibility of carbon black is poor and abrasion resistance is lowered. Further, when silica is compounded, there is a problem that grip performance at a high temperature and abrasion resistance are lowered.
In order to improve these points, JP-A-2005-154696 proposes that a low molecular weight styrene-butadiene copolymer is used. However, since double bonds having crosslinking property exist in the low molecular weight styrene-butadiene copolymer, a portion of a low molecular weight component forms crosslinking with a rubber of matrix, it is incorporated in the matrix, and sufficient hysteresis loss is not generated. Further, when the double bond portions are converted to saturated bonds by hydrogenation so that the low molecular weight component is not incorporated in the matrix by crosslinking, compatibility with the matrix is remarkably deteriorated, and as a result, breakage resistance property tended to be lowered and the low molecular weight component tended to breed.